Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, Virginia, USA.
Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia, USA.
Analyst. 2019 Dec 21;144(24):7326-7335. doi: 10.1039/c9an01699f. Epub 2019 Oct 30.
4-Mercaptopyridine (4-Mpy) is a pH reporter molecule commonly used to functionalize nanoprobes for surface-enhanced Raman spectroscopy (SERS) based pH measurements. However, nanoprobes functionalized by 4-Mpy alone have low pH sensitivity and are subject to interference by halide ions in sample media. To improve nanoprobe pH sensitivity and reliability, we functionalized gold nanoparticles (AuNPs) with both 4-Mpy and bromide ion (Br). Br electrostatically stabilizes protonated 4-Mpy, thus enabling sensitive SERS detection of the protonation state of 4-Mpy as a function of pH while also reducing variability caused by external halide ions. Through optimization of the functionalization parameters, including suspension pH, [4-Mpy], and [Br], the developed nanoprobes enable monitoring of pH from 2.1 to 10 with high SERS activity and minimal interference from halide ions within the sample matrix. As a proof of concept, we were able to track nanoprobe location and image the pH distribution inside individual cancer cells. This study provides a novel way to engineer reliable 4-Mpy-functionalized SERS nanoprobes for the sensitive analysis of spatially localized pH features in halide ion-containing microenvironments.
4-巯基吡啶（4-Mpy）是一种常用的 pH 报告分子，常用于功能化纳米探针，以进行基于表面增强拉曼光谱（SERS）的 pH 测量。然而，仅用 4-Mpy 功能化的纳米探针 pH 灵敏度较低，并且容易受到样品介质中卤素离子的干扰。为了提高纳米探针的 pH 灵敏度和可靠性，我们用 4-Mpy 和溴离子（Br）共同功能化了金纳米颗粒（AuNPs）。Br 静电稳定质子化的 4-Mpy，从而能够敏感地检测 4-Mpy 的质子化状态作为 pH 的函数，同时减少来自外部卤素离子的变异性。通过优化功能化参数，包括悬浮液 pH、[4-Mpy] 和 [Br]，开发出的纳米探针能够在样品基质中存在卤素离子的情况下，以高 SERS 活性和最小的干扰从 pH 2.1 监测到 10，实现可靠的检测。作为概念验证，我们能够跟踪纳米探针的位置并对单个癌细胞内的 pH 分布进行成像。本研究为工程化可靠的 4-Mpy 功能化 SERS 纳米探针提供了一种新方法，用于在含有卤素离子的微环境中对空间局部化的 pH 特征进行敏感分析。
